Tribological behavior of surface-modified layers on Ti alloy

Ti alloy (Ti-6Al-4V) was surface-modified by immersing in the NaOH solution, being coated with sol-gel TiO₂ film, and thermal oxidization at 500°C. The friction and wear behaviors of the surface modified layer on the Ti alloy in dry sliding against SAE52100 steel were evaluated on a unidirectional friction coefficient procession measurement apparatus. The chemical states of some typical elements in the modified layers were examined with an X-ray photoelectron spectrometer. As a result, the wear resistance and friction reduction of Ti alloy was effectively improved by immersing in the NaOH solution, which was attributed to the formation of TiO₂ layer on the modified Ti alloy surface. The sol-gel TiO₂ coating on the Ti alloy showed fair wear-resistance at 1 N load but poor wear-resistance at 3 N load, which was attributed to the existence of Al₂O₃ in the modified surface. The Ti alloy after being treated with hot NaOH solution showed the improved friction-reducing and antiwear behavior, while the toxic Al entrapped in the surface layer was removed by its reaction with the NaOH solution, thus the treatment of Ti alloys with the NaOH solution could find the promising application in the surface modification of Ti alloys for the medical use.